The media buying arm of WPP said in its "This Year, Next Year: UK Media and Marketing Forecasts" report that total UK adspend is expected to grow 6.3% to £14.9bn this year, rising another 5.7% to £15.7bn in 2015.
Within the 2015 total, digital adspend is forecast to break through the £8bn mark to £8.1bn, a rise of 13% on 2014 when online spend is expected to be £7.1bn.
Those countries that are most likely to follow the UK's digital lead in 2015 are Sweden, where 47% of total adspend will be digital, Denmark (43%), Australia (42%) and Norway (40%), the Guardian reported.
Adam Smith, futures director at GroupM, attributed the rise of digital in the UK to enthusiasm for online shopping in the country and widespread use of mobile devices.
"The British are the most enthusiastic online shoppers in the world in terms of spend per head and there has always been a high level of credit and debit card use [online]," he said.
"On top of that Britons have rapidly embraced smartphone and tablet use, all of which has fuelled where advertisers spend their money," he added.
Turning to the outlook for other media in 2014, the report found traditional TV is continuing to hold steady, attracting a projected £3.9bn, or 26%, of total adspend.
But, Smith noted: "The longer-term question is whether online will wrest investment from TV with the ease it did from press media. This is a fairer fight, which will unleash creativity and force scrutiny of simple broadcast versus 'addressability at scale'".
Print media remain under the most pressure, the report said, with 2014 adspend in physical newspapers and magazines expected to fall below £2.5bn, a decline of 9% from 2013. And it is expected to fall a further 9% in 2015 to £2.3bn.
The Expenditure Report, published by Warc on behalf of the UK Advertising Association, expects total advertising expenditure to rise 6.4% this year and a further 6.5% in 2015. By the end of the forecast period, digital will account for two in every five pounds spent on advertising in the UK.
Data sourced from GroupM, Guardian; additional content by Warc staff